The invention relates to a steering gear according to the introductory part of claim 1, and also according to the introductory part of claim 2. Such a gear is known from German patent application 36 07 691.
For different agricultural tilling operations, it is important that an implement be moved along a predetermined path with great precision. Examples of such operations are hoeing and row-spraying, where the implement, which may for instance carry several hoes or spraying nozzles, must be controlled with very slight lateral deviations relative to the rows of plants, to enable hoeing close along the plants without damaging them or to succeed with a narrow spraying track without missing any plants or at least parts thereof. Normally, row-cultivated plants are arranged in rows that are as straight as possible, so that during the operation, steering is usually limited to minor steering corrections or following faint curves around mountain slopes and obstacles or on headlands.
To obtain a very taut course of the implement, it is known to provide the implement with tracking guides, such as tracking disks, wheels with tires or slides, which engage the soil and prevent lateral movements of the steerable part and the implements relative to the soil. However, the implement must steer along with the tractor, so that the implement remains steerable by the tractor.
In the construction known from the above German patent application 36 07 691, the transmission structures are of such design that the steerable part of the gear and the implement connected thereto can swivel about an imaginary point of rotation located before the point where the aggregated forces exerted by the soil on the implement act on that implement. As a result, the implement steers leftwards in reaction to a lateral movement to the right relative to the tractor and vice versa, so that it is centered relative to the imaginary point of rotation and can follow steering movements of the tractor, just like a trailer traveling behind a tractor, which trailer is hitched to that tractor for pivoting around a ball of a towing hook.
When such a steerage is used, the course of the implement along an intended path still proves to be insufficiently accurate for different applications, such as hoeing. Sometimes, the implement swerves out spontaneously. In itself, this already forms an adverse deviation from the intended path and moreover often causes the operator to perform steering corrections which, in combination with the implement following the imaginary point of rotation, cause an oscillating movement of the actual path around the ideal path. In particular, if the operator steers less adequately, it will take some time before the ideal path is followed sufficiently accurately again. In particular for the tilling operations discussed, which require great precision, the steering gears known from these patent applications therefore prove to be inadequate.
It is an object of the invention to provide a gear which allows an intended straight or faintly curved path to be followed more accurately, but which can still follow steering movements induced by the tractor. In accordance with the invention, this object is realized by designing a steerage of the type indicated hereinabove according to the characterizing part of claim 1 and/or according to the characterizing part of claim 2.
Because during lateral movements of the steerable part, the steerable part on the side of the other one of the engagement positions moves backwards less than in the known gear, the influence of uneven rearwardly directed loads on is the implement on those lateral displacements of the implement is substantially limited or practically eliminated Such uneven loads on the implement may for instance be caused when the soil on the left-hand side of the tractor offers more resistance than the soil on the right-hand side of the tractor.
Nevertheless, due to the forward movement at one of the engagement positions, lateral movements of the implement relative to the tractor, which are for instance caused by steering movements of the tractor, do result in such steering movements of the steerable part and the implement attached thereto, that the implement sufficiently steers along with the tractor and in each case sufficiently returns into a position located centrally before the tractor. When the tractor is for instance steered through bends, the steering of the bend imposes a lateral movement of the steerable part with the implement relative to the yoke structure and the tractor. This movement of the tractor forces the steerable part and the implement to steer the same bend, while the lateral force required for effecting this can be controlled by means of the steerage of the tractor.
During steering movements to the left, the steerable part and the implement attached thereto rotate about a point of rotation or at least about momentary points of rotation at a distance to the left of the central longitudinal plane, and during steering movements to the right, they rotate about a different point of rotation or at least about other momentary is points of rotation at a distance to the right of the central longitudinal plane. Since in steering movements from the central position, the point of rotation about which the steerable part rotates is located immediately at a distance to the left or right of the central longitudinal plane, a steering movement and possibly an associated lateral movement of the steerable part are only induced in the case of a highly uneven distribution of loads over the width of the implement. Consequently, in the gear proposed, lateral movements of the implement due to such loads that are unevenly distributed over the width of the implement hardly occur, if at all.
Because of the reduced influence of external load variations on the movements of the steerable part of the coupling and the implement relative to the yoke structure, the accuracy with which, during the tilling operation, the intended path can be followed is improved considerably.
In the dependent claims, particularly advantageous embodiments of the invention are laid down.